In the agricultural field there are employed devices for attachment of agricultural accessories to tractors in the form of a pair of long bars provided with eyelets at the ends thereof. The eyelets form ball joints when attached to the pins of the tractor and of the accessory. In general these bars are rigid, which renders difficult the attachment thereof when the tractor is not parked at the exact distance of the accessory which is required for the engagement. However, there exist certain bars designated as extensible or telescopic that allow the attachment in such cases, due to their ability to disassemble an end thereof and extend the same until the point of engagement of the accessory without however disconnecting the same from the rest of the bar. In order to reassemble the bar and render the same rigid, it is necessary that the tractor driver moves the tractor backwards, until the bar reaches its initial position and remain thereat due to the action of an automatic spring-loaded latch.
There is known in the art, for example, the French patent document number FR 2 715 893-A3 that refers to an extensible bar made out of two elements: one in the form of a bar that is attached to the tractor by a spherical eyelet and another element in the form of a sleeve, also provided with an eyelet at the end thereof. The bar fits within the sleeve and is locked therein by a pin that extends through the two parts passing through orifices in the sleeve and through a slot provided in longitudinal alignment in the bar. Thereby the bar is allowed to slide longitudinally within the sleeve along a path equivalent to the length of the slot. In the bar there is also a U-shaped space near the slot wherein is accommodated a latch that slides perpendicularly to the bar within a chamber in the upper part of the sleeve, to inhibit the telescopic movement when the assembly is in the operating position. The latch is kept pressed against the bar by helical springs and is removed by pulling a pin that crosses the sleeve chamber. The latch may be kept in the retracted position by a blocking system actuated by the rotation of the pin around the axis thereof, thus facilitating the detachment of the device.
The technique described in this document requires a large number of components to form the mechanism that actuates the latch comprised of two springs, a pin, a latch, a cover-shaped plate, four bolts, and a grease nipple, in addition to a plate that forms the chamber that is welded to the sleeve. Both the quantity and the process of manufacture of these components contribute to a high cost of production of the assembly.
There exist in the art other patent documents relative to extensible bars, such as, for example, Brazilian patent application No. BR PI9905125-7A, which refers to an extensible bar with an equally complex locking system.